The semiconductor integrated circuit industry has experienced rapid growth in the past several decades. Technological advances in semiconductor materials and design have produced increasingly smaller and more complex circuits. These material and design advances have been made possible as the technologies related to processing and manufacturing have also undergone technical advances. In the course of semiconductor evolution, the number of interconnected devices per unit of area has increased as the size of the smallest component that can be reliably created has decreased.
Many of the technological advances in semiconductors have occurred in the field of memory devices, and some of these involve capacitors. Additionally, capacitors may be used in other applications on an integrated circuit (IC), including for signal conditioning. During the operation of certain circuits, power supply lines may supply transient currents with a relatively high intensity. These conditions can result in noise on the power supply lines. Specifically, the voltage on the power supply line may fluctuate when the transition time of the transient current is particularly short or when the line's parasitic inductance or parasitic resistance is large. To ameliorate such conditions, filtering or decoupling capacitors may be used, acting as temporary charge reservoirs to prevent momentary fluctuations in supply voltage.
Integrating decoupling capacitors into certain systems-on-chip (SOCs), particularly those involving certain types of memory, may entail a number of problems. For example, some decoupling capacitors may suffer from capacitance variations caused by the doping characteristics of the polysilicon capacitor electrode plates. These devices can exhibit fairly large changes in capacitance as a function of applied voltage, thus having a large voltage coefficient of capacitance, and may have problematic parasitic effects. Decoupling capacitors on certain SOCs have not been entirely satisfactory to date and may pose increasing problems in the future.
The various features disclosed in the drawings briefly described above will become more apparent to one of skill in the art upon reading the detailed description below. Where features depicted in the various figures are common between two or more figures, the same identifying numerals have been used for clarity of description.